The present invention relates to a hybrid carbon/carbon composite suitable for use as a friction material for high speed and heavy duty brakes in automobiles, trucks, shinkansen, aircrafts, etc. and a method of manufacture thereof.
It is known that carbon is one of the most excellent heat resistant materials. And, one type of carbon material is a carbon/carbon composite which is reinforced by high-strength carbon fibers and modified by heat treatment (hereinafter abbreviated simply as C/C composite).
Since the C/C composite has a high specific strength and an excellent heat resistance, it is suitable for use as a friction material for brakes used, in particular, for aircrafts.
At the present time, as a method for obtaining such C/C composite, suitable for use as a friction material as shown in FIG. 5, filler (indicated by F in the diagram) such as coke etc. to form a matrix and a binder (indicated by B in the diagram) such as thermosetting resin etc. are mixed, carbon fibers (indicated by CF in the diagram) are added to the mixture, and then resin impregnation is performed for molding. This molded object is subjected to heat treatment to carbonize and/or graphitize the binder, thereby to form the composite. However, when carbonizing by heat treatment, binder is partially decomposed thermally and gasified, so that pores are generated in the matrix. These pores bring not only a decrease in the strength of the composite, but also a generation of introductory pits for oxygen when the composite is used as a friction material for brakes to cause oxidation wear at high temperature resulting in deterioration and further decrease in strength.
For solving this inconvenience, at present, such procedure that the same kind of thermosetting resin as binder is impregnated into the pores and the carbonization thereof is performed is repeated three to seven times to decrease the porosity of the C/C composite.
In the present friction material comprising C/C composite, in order to obtain high density thereof and excellent adhesion between carbon fibers and binder, a method called chemical vapor deposition (indicated by CVD in FIG. 5) is adopted, wherein hydrocarbon gases such as methane, propane, etc. are decomposed thermally at 1000.degree. to 1200.degree. C. in a furnace under vacuum or reduced pressure, so that the decomposed atomic carbon is allowed to intrude into remaining pores of the C/C composite.
For this reason, it takes a term of three to four months for obtaining the product, so that the price of product becomes remarkably expensive. Hence, it is the status quo that there is limited application except for special purposes.
Moreover, one of the inventors previously introduced an invention in Japanese Un-examined Patent Publication No. SHO 60-200867, wherein meso-phase carbon and carbon fibers or graphite fibers are mixed, molded and subjected to heat treatment to obtain a C/C composite. In this application, however, mixing of more than two kinds of carbon fibers with different length with meso-phase carbon is not embodied, further the content of carbon fibers in the previous invention is much less than that in the present invention, so that the strength of the composite is low.
As a result of extensive investigations in view of this situation, a method of manufacturing a highly strengthened C/C composite, which need not impregnation and vaporization each causing an increase in cost, is offered. According to the present invention, a complicated manufacturing process extending over a long period of time is simplified and shortened, and further a hybrid C/C composite having a strength and heat resistance equivalent to a conventional one and being low in price has been developed.